The present invention is concerned with methods for promoting the transfer of elementary particles across a potential energy barrier.
In Edelson""s disclosure, filed Mar. 7, 1995, titled xe2x80x9cElectrostatic Heat Pump Device and Methodxe2x80x9d, Ser. No. 08/401,038, now abandoned, assigned to the same assignee as the present invention and incorporated herein by reference in its entirety, two porous electrodes were separated by a porous insulating material to form an electrostatic heat pump. In said device, evaporation and ionization of a working fluid in an electric field provided the heat pumping capacity. The use of electrons as the working fluid is disclosed in that application. In Edelson""s subsequent disclosure, filed Jul. 5, 1995, titled xe2x80x9cMethod and Apparatus for Vacuum Diode Heat Pumpxe2x80x9d, Ser. No. 08/498,199, now U.S Pat No. 6,089,316 assigned to the same assignee as the present invention, an improved device and method for the use of electrons as the working fluid in a heat pumping device is disclosed. In this invention, a vacuum diode is constructed using a low work function cathode.
In Edelson""s further subsequent disclosure, filed Dec. 15, 1995, titled xe2x80x9cMethod and Apparatus for Improved Vacuum Diode Heat Pumpxe2x80x9d, U.S. Pat. No. 5,722,242, assigned to the same assignee as the present invention and incorporated herein by reference in its entirety, the work function of the anode was specified as being lower than the work function of the cathode in order to optimize efficient operation.
In a yet further subsequent disclosure, filed Dec. 27, 1995, titled xe2x80x9cMethod and Apparatus for a Vacuum Diode Heat Pump With Thin Film Ablated Diamond Field Emissionxe2x80x9d, Ser. No. 08/580,282, now abandoned assigned to the same assignee as the present invention and incorporated herein by reference in its entirety, Cox and Edelson disclose an improvement to the Vacuum Diode Heat Pump, wherein a particular material and means of construction was disclosed to further improve upon previous methods and devices.
The Vacuum Diode at the heart of Edelson""s Vacuum Diode Heat Pump may also be used as a thermionic generator: the differences between the two devices being in the operation of the diode, the types and quantities of external energy applied to it, and the provisions made for drawing off, in the instance of the thermionic converter, an electrical current, and in the instance of the Vacuum Diode Heat Pump, energy in the form of heat.
In Cox""s disclosure, filed Mar. 6, 1996, titled xe2x80x9cMethod and Apparatus for a Vacuum Thermionic Converter with Thin Film Carbonaceous Field Emissionxe2x80x9d, Ser. No. 08/610,599, now abandoned, assigned to the same assignee as the present invention and incorporated herein by reference in its entirety, a Vacuum Diode is constructed in which the electrodes of the Vacuum Diode are coated with a thin film of diamond-like carbonaceous material. A Vacuum Thermionic Converter is optimized for the most efficient generation of electricity by utilizing a cathode and anode of very low work function. The relationship of the work functions of cathode and anode are shown to be optimized when the cathode work function is the minimum value required to maintain current density saturation at the desired temperature, while the anode""s work function is as low as possible, and in any case lower than the cathode""s work function. When this relationship is obtained, the efficiency of the original device is improved.
Many attempts have been made to find materials with low work function for use as cathodes for vacuum diodes and thermionic energy converters. Currently most research is in the field of cathodes for vacuum tubes. Research in thermionic converter technology is less intensive because of the difficulties of increasing thermionic emission of electrons from the flat surface, where field emission effect can not be applied. The practical importance of thermionic energy conversion is rapidly increasing due to increased needs for alternative energy sources. The most effective way of decreasing work function known today is the use of alkaline metal vapors, particularly cesium, and coating the emitter surface with oxide thin films. Use of Cs vapor is not without technical problems, and thin film coated cathodes generally show short lifetimes.
The thermotunnel converter is a means of converting heat into electricity which uses no moving parts. It has characteristics in common with both thermionic and thermoelectric converters. Electron transport occurs via quantum mechanical tunneling between electrodes at different temperatures. This is a quantum mechanical concept whereby an electron is found on the opposite side of a potential energy barrier. This is because a wave determines the probability of where a particle will be, and when that probability wave encounters an energy barrier most of the wave will be reflected back, but a small portion of it will xe2x80x98leakxe2x80x99 into the barrier. If the barrier is small enough, the wave that leaked through will continue on the other side of it. Even though the particle does not have enough energy to get over the barrier, there is still a small probability that it can xe2x80x98tunnelxe2x80x99 through it.
The thermotunneling converter concept was disclosed in U.S. Pat. No. 3,169,200 to Huffman. In a later paper entitled xe2x80x9cPreliminary Investigations of a Thermotunnel Converterxe2x80x9d, [23rd Intersociety Energy Conversion Engineering Conference vol. 1, pp. 573-579 (1988)] Huffman and Haq disclose chemically spaced graphite layers in which cesium is intercalated in highly orientated pyrolitic graphite to form a multiplicity of thermotunneling converters in electrical and thermal series. In addition they teach that the concept of thermotunneling converter was never accomplished because of the impossibility of fabricating devices having electrode spacings of less than 10 xcexcm. The current invention addresses this shortcoming by utilizing a piezo-electric, electrostrictive or magnetostrictive element to control the separation of the electrodes so that thermotunneling between them occurs.
A further shortcoming of the devices described by Huffman is thermal conduction between the layers of the converter, which greatly reduces the overall efficiency of these thermotunnelling converters.
In Edelson""s application filed 12th May 1997, titled xe2x80x9cMethod and Apparatus for Photoelectric Generation of Electricityxe2x80x9d, Ser. No. 08/854,302, now U.S. Pat. No. 5,973,259, assigned to the same assignee as the present invention and incorporated herein by reference, is described a Photoelectric Generator having close spaced electrodes separated by a vacuum. Photons impinging on the emitter cause electrons to be emitted as a consequence of the photoelectric effect. These electrons move to the collector as a result of excess energy from the photon: part of the photon energy is used escaping from the metal and the remainder is conserved as kinetic energy moving the electron. This means that the lower the work function of the emitter, the lower the energy required by the photons to cause electron emission. A greater proportion of photons will therefore cause photo-emission and the electron current will be higher. The collector work function governs how much of this energy is dissipated as heat: up to a point, the lower the collector work function, the more efficient the device. However there is a minimum value for the collector work function: thermionic emission from the collector will become a problem at elevated temperatures if the collector work function is too low.
Collected electrons return via an external circuit to the cathode, thereby powering a load. One or both of the electrodes are formed as a thin film on a transparent material, which permits light to enter the device. A solar concentrator is not required, and the device operates efficiently at ambient temperature.
It is well known from Quantum Mechanics that elementary particles have wave properties as well as corpuscular properties. The density of probability of finding an elementary particle at a given location is where |"psgr"|2 where "psgr" is a complex wave function and has form of the de Broglie wave:
"psgr"=A exp[(xe2x88x92i2xcfx80/h)(Etxe2x88x92pr)]xe2x80x83xe2x80x83(1)
Here "psgr" is wave function; h is Planck""s constant; E is energy of particle; p is impulse or momentum of particle; r is a vector connecting initial and final locations; t is time.
There are well known fundamental relationships between the parameters of this probability wave and the energy and impulse of the particle:
E is electron energy and p=(h/2xcfx80)kxe2x80x83xe2x80x83(2)
Here k is the wave number of probability wave. The de Broglie wavelength is given by:
xcex=2xcfx80/kxe2x80x83xe2x80x83(3)
If time, t, is set to 0, the space distribution of the probability wave may be obtained. Substituting (2) into (1) gives:
"psgr"=A exp(ikr)xe2x80x83xe2x80x83(4)
FIG. 1 shows an elementary particle wave moving from left to right perpendicular to a surface 7 dividing two domains. The surface is associated with a potential barrier, which means the potential energy of the particle changes as it passes through it.
Incident wave 1 A exp(ikx) moving towards the border will mainly reflect back as reflected wave 3 xcex2A exp(xe2x88x92ikx), and only a small part leaks through the surface to give transmitted wave 5 xcex1(x)A exp(ik""x) (xcex2≈1 greater than  greater than xcex1). This is the well-known effect known as quantum mechanical tunneling. The elementary particle will pass the potential energy barrier with a low probability, depending on the potential energy barrier height.
Usagawa in U.S. Pat. No. 5,233,205 discloses a novel semiconductor surface in which interaction between carriers such as electrons and holes in a mesoscopic region and the potential field in the mesoscopic region leads to such effects as quantum interference and resonance, with the result that output intensity may be changed. Shimizu in U.S. Pat. No. 5,521,735 discloses a novel wave combining and/or branching device and Aharanov-Bohm type quantum interference devices which have no curved waveguide, but utilize double quantum well structures.
Mori in U.S. Pat. No. 5,247,223 discloses a quantum interference semiconductor device having a cathode, an anode and a gate mounted in vacuum. Phase differences among the plurality of electron waves emitted from the cathode are controlled by the gate to give a quantum interference device operating as an AB type transistor.
Other quantum interference devices are also disclosed by Ugajin in U.S. Pat. No. 5,332,952 and Tong in U.S. Pat. No. 5,371,388.
In their U.S. patent application Ser. No. 08/924,910 filed Sep. 8, 1997, now abandoned, and Continuation in Part application Ser. No. 08/481,803 filed Aug. 31, 1998, assigned to the same assignee as the present invention and incorporated herein by reference in its entirety, Tavkhelidze and Edelson describe diode devices in which the separation of the electrodes is effected using piezo-electric positioning elements. They also teach a method for fabricating electrodes in which imperfections on one are exactly mirrored in the other, which allows electrode to be positioned very closely together.
Broadly the present invention is a method for enhancing the passage of elementary particles through a potential energy barrier utilizing interference of de Broglie waves to increase the probability of emission. This represents an improvement over all the aforementioned technologies.
In one embodiment, the invention provides an elementary particle-emitting surface having a series of indentations or protrusions. The depth of the indents (or height of the protrusions) is chosen so that the probability wave of the elementary particle reflected from the bottom of the indent interferes destructively with the probability wave of the elementary particle reflected from the surface. This results in a reduction of reflecting probability and as a consequence the probability of tunneling through the potential barrier to an adjacent surface is increased.
In another embodiment, the adjacent surface is absent. In this case, the energy spectrum of electrons becomes modified such that electrons may not tunnel out into the vacuum. This results in an increase in the Fermi level with a consequent reduction in apparent work function. The result is a surface which can be used in virtually any cathode application, including electronic circuits, antennas, imaging, amplifiers, flat-panel displays (FEDs), and all cold-cathode applications including cathode ray tubes.
In a further embodiment, the probability wave extends beyond the barrier, allowing electrons to be pumped into vacuum with a suitably applied voltage to give enhanced field effect emission.
In further embodiments, the invention provides vacuum diode devices, including a vacuum diode heat pump, a thermionic converter and a photoelectric converter, in which either or both of the electrodes in these devices utilize said elementary particle-emitting surface.
In yet further embodiments, the invention provides devices in which the separation of the surfaces in such devices is controlled by piezo-electric positioning elements.
A further embodiment provides a method for making an elementary particle-emitting surface having a series of indentations or protrusions.
Objects of the present invention are, therefore, to provide new and improved methods and apparatus for particle emission, having one or more of the following capabilities, features, and/or characteristics:
An object of the present invention is to provide a method for promoting transfer of elementary particles across a potential barrier, comprising providing a surface on which the potential barrier appears having a geometrical shape for causing de Broglie interference between said elementary particles.
An advantage of the present invention is that destructive interference between the waves of emitted particles may be created, which allows for an increase in particle emission.
A further object of the present invention is to provide an elementary particle-emitting surface having a geometrical shape for causing de Broglie interference.
An advantage of the present invention is that thermionic emission is greatly enhanced and becomes an extremely practical technology.
An object of the present invention is to provide a surface having a series of indentations (or protrusions), the depth of which is chosen so that the probability wave of the elementary particle reflected from the bottom of the indent interferes destructively with the probability wave of the elementary particle reflected from the surface.
An advantage of the present invention is that the effective work function of the material comprising the surface is reduced.